=over

=item $^M
X<$^M>

By default, running out of memory is an untrappable, fatal error.
However, if suitably built, Perl can use the contents of C<$^M>
as an emergency memory pool after C<die()>ing.  Suppose that your Perl
were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc.
Then

    $^M = 'a' x (1 << 16);

would allocate a 64K buffer for use in an emergency.  See the
F<INSTALL> file in the Perl distribution for information on how to
add custom C compilation flags when compiling perl.  To discourage casual
use of this advanced feature, there is no L<English|English> long name for
this variable.

This variable was added in Perl 5.004.

=back